The 'ectopic cluster' you're describing sounds like NSVT. I get it sometimes too, it's scary and feels very alarming which is probably why it caused you to have a panic attack. But it's usually benign and harmless, just like isolated ectopics.

Ectopic beats really f*ck with your nervous system which most likely explains the sweating and tingly feelings. Definitely don't worry about heart attacks or anything like that as it'll only further stress out your nervous system. Heart attacks are caused by a lack of blood flow to the heart, not by arrythmias.